1. Field of the Invention
The present invention relates to an airborne trailing cable-antenna which is operated in a vertical orientation in order to transmit vertically polarized electromagnetic signal energy.
2. Description of the Prior Art
It is necessary to transmit radio messages to submarines at sea. The standard method utilizes an aircraft trailing an airborne radiating antenna, wherein the antenna hangs vertically from the aircraft orbiting the ocean. The orbiting characteristics of the aircraft, and the aerodynamics of the antenna, are critical during the tuning of the antenna prior to transmission. The standard one-half wavelength antenna, dependent upon the transmitting frequency (17 kHz-60 kHz) can be in the order of 25,000 feet (7621.95 m) in length. If it is desirous to transmit at higher frequencies, the length of the trailing airborne antenna is proportionally shorter.
The deployment of a trailing airborne antenna is frequency dependent. The length of the deployed antenna must be approximately one-half wavelength of the transmitting frequency to achieve optimum tuning and resonance. In the past and with the aircraft in present use, it has been impractical to deploy a vertical trailing antenna from an aircraft at frequencies higher than 30 kHz. The antenna length at higher frequencies was too short to deploy the antenna vertically because of the aerodynamic requirements of the aircraft in flight. The shortened antenna, due to the flight pattern capabilities of the deploying aircraft and the aerodynamics of the antenna, was deployed trailing the aircraft in a horizontal mode, parallel to the ground. Electromagnetic energy transmission in the horizontal mode resulted in electromagnetic energy propagation in a horizontal polarized plane. Deployment of a trailing airborne antenna at the lower frequencies 17 to 30 kHz requires a much longer antenna. The longer antenna when deployed, dependent upon the orbital characteristics of the aircraft, transmitted electromagnetic energy in a vertical polarized plane. The aircraft, orbiting with a trailing antenna at a lower frequency, allowed the antenna to drop vertically from the aircraft and hang vertically during orbit. The electromagnetic energy was transmitted from the antenna in a vertical polarized plane resulting in electromagnetic energy propagation effective over long distances.
The problem to be solved is; the deployment of a trailing airborne antenna with sufficient antenna cable length to permit the vertical propagation of electromagnetic energy via a vertical polarized plane, when the transmission frequency to be tuned and resonated is greater than 30 kHz.
Airborne antennas have been utilized over the years. For example, U.S. Pat. No. 3,724,817 "A Long Line Loiter Technique" patented by J. C. Simmons Dec. 10, 1970 teaches a plane with a tow line tethered to the plane and a high drag device wherein the line is stalled by the drag device while the plane circles. This high drag cone slidably mounted on the line serving as a parachute or drag for the line was added to the tethered line to eliminate knotting and to hold constant the tension of the line while the plane was in the orbit mode.
U.S. Pat. No. 2,432,371 "Trailing Antenna" by F. J. Berberich patented Nov. 3, 1942 teaches only a trailing antenna improvement which allows the antenna to be reeled inward or outward without tangling within the plane's fuselage area. This was achieved by attaching a cable and weight onto the end of the antenna so that in the trailing or travel mode of the plane the extended or dispensed cable-antenna remained in a position parallel to the flight of the plane.
U.S. Pat. No. 4,110,724 "Apparatus for the Transmission of Messages by Means of Electromagnetic Means" patented by J. Peters Aug. 29, 1978 teaches an apparatus for the long range transmission of messages by means of electromagnetic waves. This apparatus consisted of a long wave transmitting plant with message storing unit, a transmitter and an antenna whose overall physical length equaled one-half the length of the emitted waves or multiples thereof. The key to this patented invention, however, was a means for hoisting the antenna which included a peripheral parachute and related gear into the air from a submarine. This entire concept evolved due to the prior art antenna being hoisted by balloons.
U.S. Pat. No. 3,823,402 entitled "Antenna Deployed from Aircraft to Contact a Body of Water for Length Reduction" by N. B. Tharp patented July 9, 1974 teaches a method and apparatus for radiating low frequency radio waves. The physical length of the antenna is reduced by one-half and the distance is one-quarter of the wavelength of the radio wave to be radiated. The antenna had suitable low resistance connection provided by a drogue and the length of the antenna depended on the height of the aircraft above water.